A lot of developers get the distinction between JOIN and SEMI-JOIN wrong. Let me explain... What are JOIN and SEMI-JOIN A little bit of relational algebra first. What is an (INNER) JOIN? An JOIN is nothing but a filtered cartesian product. And what is a cartesian product? Wikipedia explains this very nicely: for sets A … Continue reading SQL JOIN or EXISTS? Chances Are, You’re Doing it Wrong
Tag: Semi join
Semi Join and Anti Join Should Have Their Own Syntax in SQL
Relational algebra nicely describes the various operations that we know in SQL as well from a more abstract, formal perspective. One of the most common relational JOIN operations is the "equi-join" or SQL INNER JOIN. The above example "equi-joins" the ACTOR, FILM_ACTOR, and FILM tables from the Sakila database, in order to produce a new … Continue reading Semi Join and Anti Join Should Have Their Own Syntax in SQL